This is a long-shot, but try looking at your VFD with a digital camera
(cell phone). Most digital cameras can see near infrared. If you can
see the filament glowing then you know the filament is intact. If not,
you don't know for sure. You would then have to measure the filament
current somehow.
Brent
On 5/4/2020 7:20 PM, Rick Bale wrote:
Using the new logic analyzer and can see that the CPU appears to be
working. It comes out of reset 200ms after receiving it's VCC signal. And
there is data on the address and data busses. Clock signals are there. But
it's still very difficult to understand the data I'm seeing and where to
look. I keep thinking about the display that's off entirely. I need to
know if the VFD is dead. I'm not sure how to test it. I did recheck the
floating power rails and noticed some ripple on the -28V rail. It was also
only about -27V. I check it's filter cap and sure enough one of the caps
was open. Easy fix.
Does any one have any advice on how to verify a bad VFD without just
replacing it? The face plate is a work of art. I don't want to
disassemble the board as getting the LED in line again looks tedious. The
VFD is getting it's +40v, +5v and 0v. Should I expect to see something on
one spot of the VFD when it's powered up, or do I need to drive some logic
HI or LO into it?
Thanks
Rick
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